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LT1952-1_15 Datasheet, PDF (1/28 Pages) Linear Technology – Single Switch Synchronous Forward Controller | |||
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FEATURES
n Synchronous Rectifier Control for High Efficiency
n Programmable Volt-Second Clamp
n Output Power Levels from 25W to 500W
n Low Current Start-Up
(LT1952: 460µA; VIN On/Off = 14.25V/8.75V)
(LT1952-1: 400µA; VIN On/Off = 7.75V/6.5V)
n True PWM Soft-Start
n Low Stress Short-Circuit Protection
n Precision 107mV Current Limit Threshold
n Adjustable Delay for Synchronous Timing
n Accurate Shutdown Threshold with Programmable
Hysteresis
n Programmable Slope Compensation
n Programmable Leading Edge Blanking
n Programmable Frequency (100kHz to 500kHz)
n Synchronizable to an External Clock up to 1.5 ⢠fOSC
n Internal 1.23V Reference
n 2.5V External Reference
n Current Mode Control
n Small 16-Pin SSOP Package
APPLICATIONS
n Telecommunications Power Supplies
n Industrial and Distributed Power
n Isolated and Non Isolated DC/DC Converters
LT1952/LT1952-1
Single Switch Synchronous
Forward Controller
DESCRIPTION
The LT®1952/LT1952-1 are current mode PWM controllers
optimized to control the forward converter topology, using
one primary MOSFET. The LT1952/LT1952-1 provide
synchronous rectifier control, resulting in extremely
high efficiency. A programmable Volt-Second clamp
provides a safeguard for transformer reset that prevents
saturation. This allows a single MOSFET on the primary
side to reliably run at greater than 50% duty cycle for high
MOSFET, transformer and rectifier utilization. The devices
include soft-start for controlled exit from shutdown and
undervoltage lockout. A precision 107mV current limit
threshold, independent of duty cycle, combines with soft-
start to provide hiccup short-circuit protection. The LT1952
is optimized for micropower bootstrap start-up from high
input voltages. The LT1952-1 allows start-up from lower
input voltages. Programmable slope compensation and
leading edge blanking allow optimization of loop bandwidth
with a wide range of inductors and MOSFETs. Each device
can be programmed over a 100kHz to 500kHz frequency
range and the part can be synchronized to an external
clock. The error amplifier is a true op amp, allowing a wide
range of compensation networks. The LT1952/LT1952-1
are available in a small 16-pin SSOP package.
L, LT, LTC and LTM are registered trademarks and ThinSOT is a trademark of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
36V to 72V Input, 12V at 20A Semi-Regulated Bus Converter
SUPPLY FROM BIAS
WINDING OF T1
40k VIN
T1
PA0905
16V
10µF
52.3k
VREF
VIN
COMP
VIN
340k
SS_MAXDC
OUT
LT1952/ OC
LT1952-1
ISENSE
Si7450
0.005Ω
Si7370
Ã2
100k
13k
SD_VSEC
FB
SYNC
SOUT
LTC3900
FG CG
T2
SYNC
GND
ROSC
220pF
560Ω
L1
PA1494.242
VOUT
12V
20A
47µF
16V
PH4840
Ã2
X5R
Ã2
0.1µF 0.1µF
PGND BLANK DELAY
40k 40k 178k
1952 TA01
12V Bus Converter
VOUT vs VIN
16
14
12
10
8
36 42 48 54 60 66 72
VIN (V)
1952 TA01b
19521fe
1
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